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The Fusion-Fission Hybrid What is it? A Fusion-Fission Hybrid (FFH) is a sub-critical fission reactor with a variable strength fusion neutron source. Mission? Supporting the sustainable expansion of nuclear power worldwide by helping to close the nuclear fuel cycle.

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Rationale for FFH Fast Burner Reactors Fast Burner Reactors could dramatically reduce the required number of high-level waste repositories by fissioning the transuranics in LWR SNF. The potential advantages of FFH burner reactors over critical burner reactors are: 1) fewer reprocessing steps, hence fewer reprocessing facilities and HLWR repositories a would be needed---no criticality constraint, so the TRU fuel can remain in the FFH for deeper burnup to the radiation damage limit. 2) larger LWR support ratio---FFH can be fueled with 100% TRU, since sub-criticality provides a large reactivity safety margin to prompt critical, so fewer burner reactors would be needed. a separation of transuranics from fission products is not perfect, and a small fraction of the TRU will go with the fission products to the HLWR on each reprocessing.

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Relation Between Fusion and Fission Power Sub-critical operation increases fuel residence time in Burner Reactor before reprocessing is necessary As k decreases due to fuel burnup, Pfus can be increased to compensate and maintain Pfis constant. Thus, sub-critical operation enables fuel burnup to the radiation damage limit before it must be removed from the reactor for reprocessing.

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Sub-critical operation provides FFH a much larger margin of safety against accidental prompt critical power excursions, allowing use of 100% transuranic fuel in FFH, but requiring a mixture of U and TRU fuel in critical reactor. Neutron density in critical reactor satisfies In sub-critical FFH reactor

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Choice of Fission Technologies for FFH Fast Burner Reactor Sodium-cooled fast reactor is the most developed burner reactor technology, and most of the world-wide fast reactor R&D is being devoted to it (deploy 15-20yr). 1.The metal-fuel fast reactor (IFR) and associated pyroprocessing separation and actinide fuel fabrication technologies are the most highly developed in the USA. The IFR is passively safe against LOCA & LOHSA. The IFR fuel cycle is proliferation resistant. 2.The sodium-cooled, oxide fuel FR and aqueous separation technologies are highly developed in France and Russia, and also in Japan and the USA. Gas-cooled fast reactor is a much less developed backup technology. 1.With oxide fuel and aqueous reprocessing. 2.With TRISO fuel (burn and bury). Radiation damage would limit TRISO in fast flux, and it is probably not possible to reprocess. Other liquid metal coolants, Pb, Pb-Bi, Pb-Li, Li. Molten salt fuel would simplify refueling, but there are issues. (Molten salt coolant only?)

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Choice of Fusion Technologies for the FFH Fast Burner Reactor The tokamak is the most developed fusion neutron source technology, most of the world-wide fusion physics and technology R&D is being devoted to it, and ITER will demonstrate much of the physics and technology performance needed for a FFH (deploy 20-25 yr). Other magnetic confinement concepts promise some advantages relative to the tokamak, but their choice for a FFH would require a massive redirection of the fusion R&D program (not presently justified by their performance). 1.Stellarator, spherical torus, etc. are at least 25 years behind the tokamak in physics and technology (deploy 40-50 yr). 2.Small Mirror (GDT) could probably be deployed in 20-25 years, but would require redirection of the fusion R&D program into a dead-end technology that would not lead to a fusion power reactor.

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SABR FFH DESIGN APPROACH Use physics, technologies, designs and design criteria that have been developed for IFR and ITER, as much as possible, so that operation of an IFR and of ITER will prototype FFH. Be conservative to allow for uncertainties i) modest plasma parameters, power density, etc. ii) 99% transuranic-fission product separation efficiency (99.9% achieved in lab).

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FUEL CYCLE IMPLICATIONS SABR FFH BURNER REACTORS A SABR TRU-burner reactor would be able to burn all of the TRU from 3 LWRs of the same power. A nuclear fleet of 75% LWRs (% nuclear electric power) and 25% SABR TRU-burner reactors would reduce geological repository requirements by a factor of >10 relative to a nuclear fleet of 100% LWRs. A SABR MA-burner reactor would be able to burn all of the MA from 25 LWRs of the same power, while setting aside Pu for future fast reactor fuel. A nuclear fleet of 96% LWRs and 4% SABR MA-burners would reduce HLWR needs by a factor of 10.

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Fusion Technology Advances Beyond ITER FFH must operate with moderately higher surface heat and neutron fluxes and with much higher availability than ITER. PROTODEMO must operate with significantly higher surface heat and neutron fluxes and with higher availability than ITER. PROTODEMO and FFH would have similar magnetic field, plasma heating, tritium breeding and other fusion technologies. PROTODEMO and FFH would have a similar requirement for a radiation-resistant structural material to 200 dpa. FFH would require the integration of fusion and fission technologies.

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PROs & CONs of Supplemental FFH Path of Fusion Power Development Fusion would be used to help meet the world’s energy needs at an earlier date than is possible with ‘pure’ fusion power reactors. This, in turn, would increase the technology development and operating experience needed to develop economical fusion power reactors. FFHs would support (may be necessary for) the full expansion of sustainable nuclear power in the world. An FFH will be more complex and more expensive than either a Fast Reactor (critical) or a Fusion Reactor. However, a nuclear fleet with FFHs and LWRs should require fewer Burner Reactors, reprocessing plants and HLWRs than a similar fleet with critical Fast Burner Reactors.